The present invention relates to novel and improved systems and apparatus for detecting an attempt to tamper with or remove the housing of a condition detecting apparatus. More particularly, the present invention relates to tamper-proof apparatus and systems for generating a detectable alarm in the presence of an unauthorized attempt to remove a condition detecting device from its normal mounting position. The present invention as will be described in detail in conjunction with a smoke detector is particularly useful for discouraging tampering or pilferage of smoke detectors or other self-containing alarm generating devices from their normal mounting environment.
The use of devices for sensing an abnormal condition such as smoke, intruders or the like for various environments including residential, commercial and other applications has come into increasing demand. This is especially true of smoke detectors as a result of the number of lives saved by generation of an audible warning alarm in the presence of a fire. Still further, the art of such smoke detectors has advanced to the point that self-contained and self-powered units are now generally available which devices do not require separate wiring to power sources or remote detector stations. Further, the mounting of such self-contained units in transient public facilities, such as motels, hotels and the like has become extensive in recent years. Unfortunately, the self-contained nature of these devices has rendered it relatively easy for theft or tampering with such devices without any means of detecting that such unauthorized efforts are in progress. Obviously such activities significantly reduce the life/safety protection available to occupants if allowed to go undetected.
Various efforts have been undertaken to provide warning signals when unauthorized removal of housings for different apparatus has occured. For instance, Whalen et al. U.S. Pat. No. 3,710,371 shows a mercury switch arrangement for triggering a silicon-controlled rectifier latching circuit to generate an alarm when an unauthorized removal attempt is made. Such mounting orientation dependent devices are not acceptable since devices such as smoke detectors may be mounted in any vertical or horizontal position.
Various other arrangements wherein plunger-type switches are actuated so as to generate an alarm have been suggested in the past. For instance, Kaplan U.S. Pat. No. 3,110,892 employs a plunger switch under the locking hasp of an enclosure so that any tampering with these hasps closes the plunger switches and actuates an alarm with the enclosure via powering from a battery pack likewise within the enclosure. Somewhat similar teachings are present in Bennett et al. U.S. Pat. No. 3,685,037 which suggests use of a separate box intended for placement beneath an item to be protected such as a typewriter or the like with an outwardly biased plunger so that removal of the weight of the typewriter or lifting of the box will close an alarm switch to actuate a buzzer contained within the housing. Yet another apparatus is shown in Bach U.S. Pat. No. 3,858,193 which generates an alarm for detection at a remote location by using a plunger switch arranged to abut an adjacent wall when the housing is screwed into the wall or mounting plate. That is, removal of the housing from the wall releases the plunger and closes an alarm switch.
Unfortunately, the plunger type of alarm switch mechanism is defeated by relatively simple efforts such as by merely sliding a stiff ruler, card or the like between the wall or surface so that the device can be removed without detecting that it is not longer in its intended position. Therefore there has been a continuing need for a pilferage or tamper-proof detector apparatus and system which will reliably generate an alarm in a manner which cannot be easily defeated as is possible with the existing prior art devices.